The present invention relates to a contact arrangement for a vacuum switch including a pair of identically configured switch contacts which are movable opposite to one another along a switch axis, and more particularly to such a contact arrangement in which each contact is composed of a contact plate and a coil body so as to generate an axial magnetic field, with the winding sections of the coil body extending circumferentially parallel to the contact plate and each winding section being connected at a first end with the contact plate and at a second end, by means of an approximately radial conductor section, with a contact pin which connects the switch contact with a switch terminal.
Such a contact arrangement is disclosed in German Patent No. 2,443,141 and corresponding U.S. Pat. No. 3,946,179. According to those patents, the axial magnetic field in each switch contact, which favorably influences switching behavior, is generated by a coil body installed between the contact pin and the contact plate. The coil body is composed of several, for example four, radial conductor sections which have their inner ends connected with the contact pin and their outer ends with arcuate winding sections which extend in the circumferential direction and are separated from one another by narrow gaps. The winding sections are followed by axially extending short conductor sections to which the common contact plate is fastened, for example by soldering, so as to conduct current.
In order to limit eddy currents, the contact plates of both switch contacts are subdivided by radially oriented slots which begin at the circumference. On the side facing away from the gap, each slot is disposed next to an axial conductor section. In the prior art contact arrangement, the radial conductor sections of the two switch contacts are arranged on top of one another when seen parallel to the axis of the switch, while the winding sections of both contacts are oriented in such a way that current passes through them in the same circumferential direction.
In the switched-on state of the prior art vacuum switch, the contact plates of both switch contacts touch one another at many locations (contact points) under the influence of a strong contact spring. The current threads emanating from these contact points initially travel within the contact plate to one of the four connection locations with the respective axial conductor sections and from there in a bundle through the respective axial conductor section and the subsequent winding section as well as the radial conductor section to the contact pin. FIGS. 6 and 7 of German Patent No. 2,443,141 indicate that, particularly if the contact plates are slotted, long current threads are produced within the contact plates even for contact points near the edge. Due to their high specific electrical resistance, these long current threads generate considerable heat in the contact plate. The current carrying capability of the contacts is further influenced by the fact that the sum of all current threads must pass through the entire length of the four winding sections of each coil body and through the associated soldering locations which act as bottlenecks for the current.
During the time an electric arc burns, the current threads in the contact plates and in the winding sections of the coil bodies flow in the same manner as in the contacted state of the contacts. For part of the current threads, the direction of the current is opposite to that of the closest winding section and cancels out its effect in the induction of the axial magnetic field. This results in a weakening of the magnetic field particularly in the region near the edge of the contact.